Study the Glorious Qur'an from AL-HAMD to WANNAS.
You will not find a single verse ordaining punishment for blasphemy.
Then go to Hadith and you will find them contradicting each other. Most of them teach acquittal on repentance.
Finally, the exalted prophet never took revenge for personal reasons or for insulting, even persecuting him. Did he not forgive all Meccans on the conquest of the town in 629? "LA TATHREEBA ALAIKUM AL-YAUM" (There is no blame on you this day).
RAHMATALLIL'AALAMEEN [Mercy for all peoples] The exalted prophet Muhammad is (and all prophets are) beyond and above insult.